[NFC][DirectX backend] Fix crash when emit_obj for DirectX backend.

[python3kgae]

Summary

When emit-obj from clang directly, DirectX backend will hit assert caused by not initialize passes for AsmPrinter.
The fix will initialize the passes by calling createPassConfig.
Also ignore global variable which not has section in DXILAsmPrinter::emitGlobalVariable to avoid hit llvm_unreachable in DXILTargetObjectFile::SelectSectionForGlobal.

[beanz]

At first glance this seems like the wrong solution. Initialization of the DirectX target should not be initializing common LLVM code.

Are the other LLVM library initializers not being called somewhere that is causing you to hit this issue?

[beanz]

Okay, digging into this more. The issue with GCModuleInfoPass looks like a 12-ish year old bug where it was left off the list of passes initialized in InitializeCodeGen, the MachineOptimizationRemarkEmitterPass is handled there, so as long as clang is properly initializing LLVM CodeGen all you should need to do is add initializeGCModuleInfoPass to llvm::initializeCodeGen.

@bogner, does that seem right to you?

[python3kgae]

In D130856#3691062, @beanz wrote:

At first glance this seems like the wrong solution. Initialization of the DirectX target should not be initializing common LLVM code.

Are the other LLVM library initializers not being called somewhere that is causing you to hit this issue?

addPassesToGenerateCode is not called. Since we don't do real code gen.
That's where createPassConfig is called which calls initializeCodeGen.

Maybe we can initialize these passes for AsmPrinter in DirectXTargetMachine::addPassesToEmitFile instead of initalizeCodeGen which will initialize a lot of passes we don't need.

[beanz]

The DirectX backend needs to be constructing a target pass config. The bug is that our override of addPassesToEmitFile isn't creating the pass config.

[python3kgae]

Call createPassConfig to make sure passes get initialized.
Skip Global Variable which not have section when emitGlobalVariable.

[beanz]

llvm/lib/Target/DirectX/DirectXTargetMachine.cpp

75

this pass we should probably keep in the addPassesToEmitFile override. This needs to be done last before emitting an object file, so keeping it separate will reduce the likelihood of introducing errors.

[python3kgae]

Keep createDXILEmbedderPass in addPassesToEmitFile.

[beanz]

LGTM.

Please fix the title to be brief and descriptive of the change, and add an appropriate change description before merging.

llvm/lib/Target/DirectX/DirectXAsmPrinter.cpp

 
 void DXILAsmPrinter::emitGlobalVariable(const GlobalVariable *GV) {
   // If there is no initializer or the section is implicit, do nothing
   if (!GV->hasInitializer() || GV->hasImplicitSection())
     return;
   // Skip the LLVM metadata
   if (GV->getSection() == "llvm.metadata")
     return;
+  if (!GV->hasSection())
+    return;
   SectionKind GVKind = TargetLoweringObjectFile::getKindForGlobal(GV, TM);
   MCSection *TheSection = getObjFileLowering().SectionForGlobal(GV, GVKind, TM);
   OutStreamer->switchSection(TheSection);
   emitGlobalConstant(GV->getParent()->getDataLayout(), GV->getInitializer());
 }
 
 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeDirectXAsmPrinter() {
   RegisterAsmPrinter<DXILAsmPrinter> X(getTheDirectXTarget());
 }

llvm/lib/Target/DirectX/DirectXTargetMachine.cpp

public:
   DirectXPassConfig(DirectXTargetMachine &TM, PassManagerBase &PM)
       : TargetPassConfig(TM, PM) {}
 
   DirectXTargetMachine &getDirectXTargetMachine() const {
     return getTM<DirectXTargetMachine>();
   }
 
   FunctionPass *createTargetRegisterAllocator(bool) override { return nullptr; }
+  void addCodeGenPrepare() override {
+    addPass(createDXILOpLoweringLegacyPass());
+    addPass(createDXILPrepareModulePass());
+    addPass(createDXILTranslateMetadataPass());
+  }
 };
 
 DirectXTargetMachine::DirectXTargetMachine(const Target &T, const Triple &TT,
                                            StringRef CPU, StringRef FS,
                                            const TargetOptions &Options,
                                            Optional<Reloc::Model> RM,
                                            Optional<CodeModel::Model> CM,
                                            CodeGenOpt::Level OL, bool JIT)
     : LLVMTargetMachine(T,
                         "e-m:e-p:32:32-i1:32-i8:8-i16:16-i32:32-i64:64-f16:16-"
                         "f32:32-f64:64-n8:16:32:64",
                         TT, CPU, FS, Options, Reloc::Static, CodeModel::Small,
                         OL),
       TLOF(std::make_unique<DXILTargetObjectFile>()),
       Subtarget(std::make_unique<DirectXSubtarget>(TT, CPU, FS, *this)) {
   initAsmInfo();
 }
 
 DirectXTargetMachine::~DirectXTargetMachine() {}
 
 bool DirectXTargetMachine::addPassesToEmitFile(
     PassManagerBase &PM, raw_pwrite_stream &Out, raw_pwrite_stream *DwoOut,
     CodeGenFileType FileType, bool DisableVerify,
     MachineModuleInfoWrapperPass *MMIWP) {
-  PM.add(createDXILOpLoweringLegacyPass());
-  PM.add(createDXILPrepareModulePass());
-  PM.add(createDXILTranslateMetadataPass());
+  TargetPassConfig *PassConfig = createPassConfig(PM);
+  PassConfig->addCodeGenPrepare();
+
   if (TargetPassConfig::willCompleteCodeGenPipeline()) {
     PM.add(createDXILEmbedderPass());
   }
   switch (FileType) {
   case CGFT_AssemblyFile:
     PM.add(createPrintModulePass(Out, "", true));
     break;
   case CGFT_ObjectFile: